340/E85/D1SC/FItech1200 big hp SB guys step inside please!

I appreciate all the replies everyone! Lots of great advice and stuff to keep me thinking about how to finish/improve the build!

MAtts440, I did consider solid but it is mostly a street car and I have seen solid mounts cause some issues on street cars with cracking K members, possibly causing block distortion etc... I have about an inch of clearance there, so I can't see the motor moving anywhere close to that on poly locks. If it does, I'm thinking I'll use a chain or something that will allow it to work with the soft material at part throttle but catch at WOT before it hits anything.

As far as the fans go, I am tempted to go flex fan because of how much air they move across the RPM band. It should do a better job at cooling the whole engine bay. The lack of significant HP loss from the electric fans and ability to control air flow at idle is tempting....it's just seems like a huge amount of amperage draw to run on a V belt...might be worth a shot though. I'm still undecided. Either way is more work- the flex fan will likely need a custom shroud to fit my thick radiator and the electric fans will require wiring.

RRvolare, that's exactly what my machinist says. He is big into small block fords and shattered the NHRA super stock GT AA record with one of his cars. He says he believes the mopar block to be every bit as strong if not stronger than the factory ford block he used to break that record at an 8.99. He didn't think I should be concerned at all about pushing it up to 12PSI or so and making around 700FWHP, especially because with the blower I won't have to spin the motor too high. I do plan on dyno tuning it prior to any street fun. I am hoping that when I downsize pulleys I won't have to relocate the tensioner (other than maybe clocking it, which just requires me to drill out a hole in the bracket for the locking pin). With a shorter belt I think it may work as is.

Only reason why I probably WON'T put the smaller pulley on right off the bat is because I don't fully trust this transmission. After a year of down time with the car and missing almost all of last year's good weather, I don't want to get greedy, push the setup too hard and end up having to down it again for the summer/fall. I think if I can manage to make 600hp on the 4.75" pulley that will be more than enough for the street and I can set the car up better to handle more power at the track next year.